1. Field of the Invention
The invention relates to a vibration generator in accordance with the preamble of claim 1.
2. Description of the Related Art
Such vibration generators are used advantageously for example in ground-compacting machines, such as for example vibration plates, and are known from EP 0 358 744 B1.
In the case of the known vibration generators two unbalanced shafts are coupled together in such a manner as to be able to rotate in opposite directions, wherein their relative phase position can be adjusted by means of a phase changing device. Each of the unbalanced shafts supports an unbalanced part which is rigidly attached to the respective unbalanced shaft, and an unbalanced part which can freely rotate on the respective unbalanced shaft over a predetermined angle range between end positions which are limited by stops. The stops are disposed with respect to the rigid unbalanced part in such a manner that the resulting total unbalance of the rigid unbalanced part and the movable unbalanced part is a maximum value in the one end position of the movable unbalanced part and is a minimum value in the other end position. The change of position of the rotatable unbalanced parts between the two end positions is effected by virtue of the fact that the direction of rotation of the unbalanced shafts is reversed, i.e. that the rotatable unbalanced parts always assume the same end position in dependence upon the direction of rotation of the unbalanced shaft which supports them.
The relative adjustment between the fixed unbalanced parts and the movable unbalanced parts changes in each case the effective resulting centrifugal force and thus the so-called mr-value (product of the resulting unbalanced mass m and the radius r of the centre of gravity of the resulting unbalanced mass). When the rigid and the movable unbalanced part are disposed on the same side of the unbalanced shaft, their centrifugal forces are summated to create a high mr-value. If, on the other hand, the movable unbalanced part is in its other end position with respect to the unbalanced shaft opposite the rigid unbalanced part, the mr-value is reduced to a minimum.
Such a vibration generator has proven itself extraordinarily well in practice. However, a disadvantage has been established, in that in order to adjust the movable unbalanced parts into the respective opposite end position it is necessary to reverse the direction of rotation of the unbalanced shafts which represents a significant technical expenditure for the drive of the unbalanced shafts. Furthermore, it is above all desirable when using the vibration generator in ground-compacting machines to be able to adjust the vibration generated by the vibration generator in an optimum manner to suit the different grounds and ground-compacting conditions even during the compacting process. Such a fine adjustment of the vibration behaviour is not possible in the case of the known vibration generators and definitely not during the operation.
A generic type-forming vibration generator is known from DE-A-12 14 616, in which are provided a first adjusting device for adjusting the phase position between a main and a part unbalanced mass on a first unbalanced shaft and a second adjusting device for adjusting the phase position between a main and a part unbalanced mass on a second unbalanced shaft, wherein the phase position can be adjusted between the first and the second unbalanced shaft by means of a phase changing device. The first and the second adjusting device are coupled to each other by way of planetary gears, so that the adjustment of the phase position between the main and part unbalanced mass on one unbalanced shaft causes a corresponding adjustment in the opposite direction of the phase position of the unbalanced masses on the other unbalanced shaft.
The object of the invention is to provide a vibration generator, whose vibration parameters, in particular the vibration amplitude and direction, can be adjusted freely and in a number of ways over wide ranges.
The object is achieved by virtue of a vibration generator in accordance with the invention according to claim 1. Advantageous further developments of the invention are evident in the dependent claims.